On 26.07.2019 16:30, Andrew Cooper wrote: > On 26/07/2019 15:22, Roger Pau Monné wrote: >> On Fri, Jul 26, 2019 at 02:52:39PM +0100, Andrew Cooper wrote: >>> Future changes are going to need to page align some percpu data. >>> >>> This means that the percpu area needs suiably aligning in the BSS so CPU0 >>> has >>> correctly aligned data. Shuffle the exact link order of items within the >>> BSS >>> to give .bss.percpu.page_aligned appropriate alignment. >>> >>> Additionally, introduce DEFINE_PER_CPU_PAGE_ALIGNED() >>> >>> Signed-off-by: Andrew Cooper <andrew.coop...@citrix.com> >>> --- >>> CC: Jan Beulich <jbeul...@suse.com> >>> CC: Wei Liu <w...@xen.org> >>> CC: Roger Pau Monné <roger....@citrix.com> >>> CC: Stefano Stabellini <sstabell...@kernel.org> >>> CC: Julien Grall <julien.gr...@arm.com> >>> CC: Volodymyr Babchuk <volodymyr_babc...@epam.com> >>> --- >>> xen/arch/arm/xen.lds.S | 5 +++-- >>> xen/arch/x86/xen.lds.S | 5 +++-- >>> xen/include/xen/percpu.h | 2 ++ >>> 3 files changed, 8 insertions(+), 4 deletions(-) >>> >>> diff --git a/xen/arch/arm/xen.lds.S b/xen/arch/arm/xen.lds.S >>> index 12c107f45d..07cbdf2543 100644 >>> --- a/xen/arch/arm/xen.lds.S >>> +++ b/xen/arch/arm/xen.lds.S >>> @@ -201,14 +201,15 @@ SECTIONS >>> *(.bss.stack_aligned) >>> . = ALIGN(PAGE_SIZE); >>> *(.bss.page_aligned) >>> - *(.bss) >>> - . = ALIGN(SMP_CACHE_BYTES); >> Don't you also need a: >> >> . = ALIGN(PAGE_SIZE); >> >> here? > > No, (I don't think so). > >> Or is the size of .bss.page_aligned also aligned to page size? > > Every object inside .bss.page_aligned should have suitable (i.e. > multiple of) size and alignment. Without this, things will break.
I'm not sure we should have such a requirement: Objects in .*.page_aligned sections should themselves have PAGE_SIZE alignment (i.e. there shouldn't be a need to ALIGN() _ahead_ of the section directive in the script (that is, the one in context above should actually be redundant). But I'm not sure about demanding their size to be a multiple of PAGE_SIZE - while C will guarantee this (and waste space in certain cases), assembly constructs could still be written such that the trailing unused space can be re-used. Otoh I agree with your virtual statement of this being a little fragile. Jan _______________________________________________ Xen-devel mailing list Xen-devel@lists.xenproject.org https://lists.xenproject.org/mailman/listinfo/xen-devel
